In direct contact steam injection heaters, steam is directly mixed with the liquid being heated, or in some cases with a slurry being heated. Direct contact steam injection heaters are very effective at transferring heat energy from steam to the liquid. They provide rapid heat transfer with virtually no heat loss to the atmosphere, and also transfer both the latent and the available sensible heat of the steam to the liquid.
The present invention was developed during ongoing developmental efforts by the assignee in the field of direct contact steam injection heaters. U.S. Pat. No. 5,622,655 entitled "Sanitary Direct Contact Steam Injection Heater And Method" by Bruce A. Cincotta et al., issuing on Apr. 22, 1997, and allowed U.S. patent application Ser. No. 08/650,648, now U.S. Pat. No. 5,842,497, entitled "Adjustable Direct Contact Steam Injection Heater", by Brian Drifka and Bruce A. Cincotta, filed on May 28, 1998, represent some of the prior developments in direct contact steam injection heaters by the assignee, and are hereby incorporated by reference.
These types of direct contact steam injection heaters use full pressure steam (i.e. the full amount of steam pressure available), and modulate the amount of steam added to the liquid for heating purposes by a nozzle and plug configuration. The steam exits through the nozzle under sonic choked flow conditions. The high speed steam from the nozzle shears the liquid into droplets, and creates a homogeneous blend of steam and liquid in a combining region located downstream of the nozzle. As heat is transferred to the liquid, the steam condenses.
Although direct contact steam injection heaters are efficient and effective, the heaters can vibrate heavily in certain specialized applications. It has been found that vibrations tend to occur when heating liquids in which steam bubbles in the mixture of liquid and steam merge to create larger bubbles of steam within the liquid before the steam condenses. The condensation of the large steam bubbles creates unwanted vibrations in the heater. This type of behavior has been noticed in liquids such as purified water (e.g. boiler feed water) which do not have a sufficient amount of nucleation points for bubble formation. It has also been noticed in liquids that do not have suitable surface tension to sufficiently atomize the liquid (e.g. oils).